JP2003124524A - High-flux led array - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-flux LED array which eliminates defects of an LED array by conventional technology. SOLUTION: The light emitting diode array includes a metal base layer, a dielectric layer arranged on the metal base layer, and a plurality of electric conductor trays arranged on the dielectric layer. A plurality of passing parts pass through the dielectric layer. The light emitting diode array further includes a plurality of light emitting diodes, which are arranged on corresponding passing parts among the passing parts and include 1st and 2nd electric contacts which are so electrically connected as to separate the electric conductive traces respectively. The respective passing parts include heat-conductive materials which are in thermal contact with the metal base layer and also in thermal contact with the corresponding light emitting diodes.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to light emitting diodes, and more particularly to an array of light emitting diodes.
y) concerning.

[0002]

2. Description of the Prior Art Arrays of light emitting diodes (LEDs) are
Various high fluxes (optical energy / optical energy / lights, such as street lights, traffic lights and LCD backlights).
Unit time) can be used in applications. In such applications, it is advantageous to increase the flux delivered per unit area of the LED array. Increasing the flux per unit area in this way is, in principle, by decreasing the spacing between LEDs in the array (and thus increasing the number of LEDs per unit area in the array) and / or individually. This is achieved by increasing the flux supplied by the LEDs of the.

[0003]

However, the LED
Any technique that increases the flux per unit area of the array typically increases the amount of heat that must be dissipated per unit area of the array to prevent significantly degrading the performance of the LED. Let

One conventional type of LED array is an LED
Each of these LED lamps includes a lamp
It comprises a die attached to a metallic leadframe within a molded or cast plastic body. The two metal leads of each lamp are typically soldered to conductive traces on a common printed circuit board of conventional design. The space occupied by the lamp's plastic body and metal leads limits the packing density of the lamps in the array. In addition, such lamps typically cannot dissipate much heat. This is because the heat generated by the lamp is dissipated primarily by the leads and conductive traces. As a result, it is not possible to drive the lamp with high current to produce a high flux.

Another conventional type of LED array is LE
The D die is a silver filled epoxy.
y) is attached to the surface of a conventional printed circuit board. Typically, LED dies are electrically connected to conductive traces on a printed circuit board using wire bonds that limit how closely they are spaced between the dies. In addition, conventional printed circuit boards on which the die is mounted are typically not effective at spreading the heat generated by the LED die. This allows the maximum operating current of the LED die, and thus the individual LE
The maximum flux obtained by the D-die is limited.

There is a need for a high flux LED array that overcomes the shortcomings of prior art LED arrays.

[0007]

An LED array according to the present invention includes a metal base layer, a dielectric layer disposed on the metal base layer, and a plurality of electrically conductive layers disposed on the dielectric layer. Including traces and. The plurality of passing portions pass through the dielectric layer. The LED array also includes a plurality of LEDs, each of the plurality of LEDs being disposed on a corresponding one of the passages and electrically separating each of the electrically conductive traces. A first electrical contact and a second electrical contact connected to. Each of the passages includes a thermally conductive material in thermal contact with the metal base layer and in thermal contact with the corresponding LED. The heat conductive material includes, for example, a solder material.

In some embodiments, the thermally conductive material in one passage is in direct physical contact with the metal substrate, in direct physical contact with the corresponding LED, or with the metal substrate. And in direct physical contact with the LED. Such direct physical contact, although sufficient, is not essential for establishing thermal contact.

The heat conductive material in the passage portion effectively provides a low thermal resistance path for heat to flow from the LED arranged on the passage portion to the metal base layer. This allows the heat to be efficiently conducted and escaped. As a result, the LEDs in the array according to the present invention can be operated at a higher current, and the LEDs can be made closer to each other than the conventional method without raising the temperature of the LEDs to a level that deteriorates the performance of the LEDs. Can be spaced apart. Thus, the LED array according to the present invention provides a larger bundle per unit area than that obtained with conventional LED arrays.

In some embodiments, the submount is located between the LED and the corresponding passage and is in direct physical contact with the thermally conductive material in the passage. By using such a submount, it becomes possible to incorporate further circuits, and
It is possible to test the LEDs before mounting them in the array.

[0011]

It should be noted that the dimensions in the attached figures do not necessarily have to a common scale. Like reference numbers in the various drawings indicate like parts in the various embodiments.

In one embodiment of the invention (FIG. 1),
The LED array 2 includes a plurality of LEDs (for example, LEDs 4) and a metal base layer 6. For a conventional conductive electrical trace layer 8, a dielectric layer 1 overlying a metallic base layer 6 is used.
Append on top of 0. Multiple transit parts (eg transit part [via]
12) passes through the trace layer 8 and the dielectric layer 10 and ends on or at the metallic base layer 6.
Each of the LEDs is arranged on the corresponding passage.

The LED 4 can be any suitable conventional light emitting diode. For example, the LED 4 may be the AlInGaN disclosed in US Pat. No. 6,133,589.
-LED or AlInGaN-LED disclosed in US patent application Ser. No. 09 / 469,657. Both of these are assigned to the assignee of the present invention,
All of which are incorporated herein by reference. In some embodiments, LED 4 may be a high flux A driven by a current greater than, for example, about 70 milliamps (mA).
lInGaN or AlInGaP-LED. For such high-bundle LEDs, for example, LumiLeds Lig
Available from hting US, LLC of San Jose, California.

LED 4 includes a conventional N contact 14 and a conventional P contact. In the embodiment shown in FIG. 1, the LED 4 is mounted as a “flip chip” with the N-type contact 14 and the P-contact 16 arranged on the same side of the LED die and oriented to face the trace layer 8. ing. N-contact 14 and P-contact 16 are reflowed to separate the conductive traces in trace layer 8.
owed) Soldered and electrically connected. LED4
Also contacts the LED 4 like contacts 14 and 16.
Of thermal contacts 20 (eg, metal pads) located on the same side of the. In some embodiments, thermal contact 20 is electrically isolated from contacts 14 and 16. Such electrical insulation is provided by, for example, the selectively provided dielectric layer 22. Other means of electrically insulating the thermal contact 20 from the contacts 14 and 16 may be used. For electrical contacts 14 and 16 and thermal contact 20, for example, suitable conventional solderable (solder)
The metal layer can be formed by a conventional method.

The passage portion 12 includes a heat conductive material 24 that is in thermal contact with the metal base layer 6 and is in thermal contact with the LED 4. The heat-conducting material 24 is, for example, a gap (li
It forms part of a continuous solid material heat flow path between the LED 4 and the metallic base layer 6, which is uninterrupted by the guidance gas filled gap. In the embodiment shown in FIG. 1, the thermally conductive material 24 is in direct contact with the thermal contact 20 of the LED 4,
Moreover, it is in direct contact with the metal base layer 6. However, in other embodiments, a thermal contact may be established between the heat-conducting material 24 and the LED 4 or metallic base layer 6 without such direct and physical contact.

In some embodiments, the thermally conductive material 24
Is or includes conventional reflowed solder applied to the passage 12 by conventional methods such as screen printing.
In such an embodiment, the thermally conductive material 24 may be the same material used as the reflowed solder 18, and the conductive material 24 and the solder 18 may be used.
Can be applied by the same processing step, and can be reflowed by the same processing step. In other embodiments, the thermally conductive material 24 is a diamond filled epoxy, a silver filled epoxy, or
Other conventional materials with high adhesion strength and good thermal conductivity can be included. In some embodiments, the thermally conductive material 24 comprises metal plated into the passage 12 by conventional methods. Such a plated metal fills the passage 12 to, for example, approximately the level of the trace layer 8. Solder reflowed by conventional methods can be applied over such plated metal in passage 12. If the heat conducting material 24 is electrically conductive, this heat conducting material may be electrically isolated from the trace layer 8 and the LED 4 by the dielectric layer 10 and the optionally provided dielectric layer 22. . If the heat conductive material 24 is a reflowable solder material, the metal base layer 6 and the thermal contact 20 are
The thickness of the heat-conducting material 24 between and is, for example, about 0.00
02 inches to about 0.005 inches, typically about 0.0
It is 01 inches.

The metal base layer 6 is selectively plated with a solderable material such as nickel or tin to obtain good mechanical and thermal contact to the thermally conductive material 24, for example. A copper plate having a thickness greater than 0.01 inch.

The metal base layer 6 can be formed from another metal or a combination of metals, and can include two or more metal layers.

In one embodiment, the trace layer 8 is of etched and plated copper that is attached to the metal base layer 6 using a conventional dielectric adhesive such as epoxy that forms the dielectric layer 10. Formed from sheets. Passages (eg, passages 12) can be formed in trace layer 8 and dielectric layer 10 using, for example, conventional mechanical tools, plasma or chemical etching, or laser ablation.

The LED array 2 may also include a lens (eg, lens 26) disposed over some or all of the LEDs to collect and direct the light emitted by the LEDs. For such lenses, see LE
It can be cast or cast by conventional methods into a clear plastic or elastomer over some or all of D. Alternatively, a small amount of silicone or similar clear material can be applied over some or all of the LEDs by conventional methods and then cured to form a simple lens, or hollow Clear lens, LE
It can be heat staked, glued or pressed onto some or all of D by conventional methods and then filled with silicone, for example to encapsulate the LED.

Thermal contact 20 and thermally conductive material 24
Can effectively provide a path with low thermal resistance for the heat to flow from the LED 4 to the metal base layer 6 and thus can effectively dissipate the heat. The thermal resistance of this path is less than the thermal resistance of the thermal path in a conventional LED array formed on a conventional printed circuit board, for example. This low resistance in the thermal path allows the LEDs in array 2 to operate at higher currents than conventional (and thus higher than conventional flux) without raising the temperature to a level that degrades performance. Can bring). Effective dissipation of heat by the heat-conducting material 24 and the metal base layer 6 allows for less spacing between LEDs than in conventional high-bundle LED arrays without overheating the LEDs and degrading their performance. Can be provided to arrange a high bundle of LEDs in the LED array 2. For each LED in the LED array 2, there is no separate molded housing, lead frame, and wire bonds to the conductive traces of the trace layer 8, thus allowing closer spacing between the LEDs. As a result, the LED array 2 can have a larger bundle per unit area than that in the conventional LED array. Since the wire bond is also removed, the LE in the present embodiment
The reliability of the D array 2 can be improved. Because wire bonds are typically the least reliable component in LED arrays.

In the second embodiment of the present invention (FIG. 2),
Each of the LEDs in the LED array 2 (eg, LED 28) is mounted on a separate submount (eg, submount 30). The submount can be made of, for example, silicon or a ceramic material. Conventional reflowed solder (eg S
The n / Pb) bump 32 electrically connects the N-type region of the LED 28 to the upper N contact 34 of the submount 30, and electrically connects the P-type region of the LED 28 to the upper P contact 36 of the submount 30. Passage 38 (40) in submount 30 comprises a conventional electrically conductive material that carries current from top N contact 34 (top P contact 36) to bottom N contact 42 (bottom P contact 44). N contact 42
And P-contacts 44 are electrically connected to separate each trace in trace layer 8 using conventional reflowed solder 18. If the submount 30 is formed of a conductive material such as silicon, then the passages 38 and 40 are dielectric tubes or liners provided in a conventional manner to prevent shorting of the passages through the submount. (Liner) can be included.

Submount 30 also includes thermal contacts 46 (eg, metal pads) applied to the backside of submount 30 adjacent electrical contacts 42 and 44. In some embodiments, thermal contact 46 is electrically isolated from contacts 42 and 44. Other means of electrically insulating the thermal contacts 46 from the contacts 42 and 44 may be used. The electrical contacts 34, 36, 42 and 44 and the thermal contact 46 can be formed, for example, by any suitable conventional solderable metal layer.

In this embodiment, the heat conducting material 24 in the passage portion 12 is in direct contact with the thermal contact 46 in the submount 30, and is in thermal contact with the LED 28 via the submount 30 and the solder bumps 32. .
In some embodiments, the reflowed solder used for the thermally conductive material 24 has a lower reflow temperature than the reflowed solder used for the solder bumps 32, which allows the submount 30 to be mounted on the LED 28 and the submount 30. It can be attached to the metal base layer 6 without interfering with the solder connection with 30. Typically LE
In order to reduce the thermal resistance imparted by the submount 30 to the heat flow from D28 to the metal base layer 6, the submount 30 is made of a thin heat conductive material.
For example, submounts formed of silicon typically have a thickness of less than about 0.010 inches.

The combination of solder bump 32, submount 30, thermal contact 46 and thermally conductive material 24 provides a low thermal resistance path for heat to flow from LED 28 to metal substrate 6. Since the thermal resistance is low as described above, the same effect as that in the above-described embodiment can be obtained. In addition, the LEDs mounted on the submount can be subjected to a preliminary test before being mounted on the LED array 2. By such a preliminary test, L
The LEDs in the ED array 2 can be selected, for example, based on well characterized values for emission wavelength and flux. In addition, the submount is an electrostatic discharge protection circuit (electros
Circuits such as tatic discharge protection circuitry can be included separately.

In the third embodiment of the present invention (FIG. 3),
There are no passages 38 and 40, and N contact 34 and P contact 36 in submount 30 are electrically connected to separate the traces in trace layer 8 by wire bonds 48 and 50, respectively. Wirebonds 48 and 50 are less expensive to make electrical connections through the transits.

In the fourth embodiment of the present invention (FIG. 4),
The trace layer 8 and the dielectric layer may be a thin conventional printed circuit board or a flex circuit attached to a metal substrate 6 having a conventional dielectric adhesive layer 54.
t) 52. A further dielectric layer 56 may be located on top of the trace layer 8. The passage portion can be formed on the printed circuit board 52 by punching, for example.

FIG. 5 schematically illustrates the placement of electrical and thermal contacts on the bottom surface of an LED assembly 58 included in an LED array according to one embodiment of the present invention. The LED assembly 58 is, for example, the LED 4
LED excluding submount such as (Fig. 1), or
LE mounted on the submount 30 (FIGS. 2 to 4)
It may include an LED mounted on a submount such as D28. The N contact 60 is, for example, LE.
It may include the N contact 14 at D4 or the lower N contact 42 at the submount 30. The P contact 62 is, for example, P in the LED 4.
The contact 16 or the lower P contact 44 in the submount 30 may be included. The thermal contact 64 is, for example, the thermal contact 20 in the LED 4,
Alternatively, thermal contacts 46 on submount 30 may be included. The thermal contacts 64 are typically
It occupies most of the bottom surface of the LED assembly 58 to facilitate heat flow to the metal substrate 6 through the thermal contacts 64.

FIG. 6 shows the LED array 2 according to one embodiment of the present invention before mounting the LED assemblies (LEDs with or without submounts) at a plurality of locations 66-1 to 66-9. It is a top view which shows typically. In each place, the passage portion (for example, the passage portion 12) exposes a part of the metal base layer 6. Also, the LED assembly 5
8 (FIG. 5) at each location to make electrical contact with each of the electrical contacts on the bottom surface of the LED assembly, such as electrical contacts 60 and 62.
Two of the conductive traces 8-1 to 8-18 (on the trace layer 8) are exposed. For the conductive electrical traces 8-1 to 8-18, some or all LEDs are connected in series, parallel or anti-parallel.
Can be interconnected to be placed in. Through holes, such as through-hole 68, are
Penetrate the metal base layer 6 and the dielectric and trace layers located above the metal base layer 6 so that a lens such as (FIG. 1) can be filled with an encapsulant such as silicone. To do.

FIG. 7 shows LED assemblies 58-1 to 58.
-9 to metal base layer 6 and conductive traces 8-1 to 8-1
7 is a top view schematically showing the LED array 2 in FIG. 6 after being attached to FIG. Each LED assembly is LE
Thermally conductive material 24 (FIGS. 1 to 4) applied to the passage located under the D assembly makes thermal contact with the metal base layer 6. In this embodiment, the LED array 2 includes nine LED assemblies (LEDs with or without submounts). Other embodiments include more or less than nine such LED assemblies.

While the invention has been described with particular embodiments, it is intended that the invention cover all modifications and alterations that fall within the scope of the appended claims. For example, the LEDs 4 and 28 shown in FIGS.
Although it is a flip chip, the present invention can use LEDs with one or more electrical contacts on the top surface. Such contacts can be wirebonded, for example, to electrical contacts on the submount or to conductive traces on a trace layer overlying the metal substrate. In addition, Figures 2-4 show one L attached to the nuclear submount.
Although only ED is shown, some embodiments may use more than one LED per submount. In such embodiments, some or all of the multiple LEDs in one submount may be
For example, they can be electrically connected in series, parallel or anti-parallel. Furthermore, the LED array according to the present invention is
It can include some LEDs applied to the submount and some LEDs directly attached to the metal substrate. Although FIGS. 1-4 show only one layer 8 of conductive traces disposed over the metal substrate 6, other embodiments can use multiple layers of conductive traces.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a part of an LED array according to a first embodiment of the present invention.

FIG. 2 is a diagram schematically showing a part of an LED array according to a second embodiment of the present invention.

FIG. 3 is a diagram schematically showing a part of an LED array according to a third embodiment of the present invention.

FIG. 4 is a diagram schematically showing a part of an LED array according to a fourth embodiment of the present invention.

FIG. 5 is a diagram schematically showing a bottom surface of an LED or an LED submount according to one embodiment of the present invention.

FIG. 6 is a top view schematically showing a part of an LED array according to one embodiment of the present invention.

FIG. 7 is a top view schematically showing the LED array shown in FIG.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shahn Harrah             United States California             94025 Menlo Park Sharon Par             Kudo Drive 1100 Condominium             # 27 (72) Inventor Douglas P. Woolverton             United States California             94043 Mountain View Wisman               Park Drive 461 F-term (reference) 5F041 AA04 AA33 CA34 DA03 DA04                       DA13 DA19 DA20 DA34 DA44                       DA57 DA82 DB08 FF11

Claims (19)

[Claims] 1. An array of light emitting diodes, comprising: a metal base layer; a dielectric layer that passes through a plurality of passages and is disposed on the metal base layer; and a plurality of dielectric layers disposed on the dielectric layer. Of electrically conductive traces and a plurality of light emitting diodes, each of the plurality of light emitting diodes being disposed on a corresponding one of the passages and having a first electrical contact. And a second electrical contact, the first electrical contact and the second electrical contact are electrically connected to separate each of the electrically conductive traces, and each of the passages is An array of light emitting diodes in thermal contact with the metal base layer and in thermal contact with the corresponding one of the light emitting diodes. 2. The array of light emitting diodes of claim 1, wherein the metal base layer has a thickness greater than about 0.01 inch. 3. At least one light emitting diode of the light emitting diodes has the first electrical contact and the second electrical contact disposed on the same surface and oriented to face the metal base layer. An array of light emitting diodes according to claim 1 including. 4. The thermally conductive material in at least one of the passages is electrically isolated from the plurality of conductive traces and the corresponding light emitting diode of the light emitting diodes. The array of light emitting diodes of claim 1 electrically isolated from the first and second electrical contacts at. 5. The array of light emitting diodes of claim 1, wherein the thermally conductive material comprises a solder material. 6. The array of light emitting diodes of claim 1, wherein the thermally conductive material in at least one of the passages is in direct contact with the corresponding light emitting diode of the light emitting diodes. 7. The array of light emitting diodes of claim 1, wherein the thermally conductive material in at least one of the passages is in direct contact with the metal substrate. 8. A heat sink disposed between a light emitting diode of one of said light emitting diodes and said corresponding one of said passages, and said heat in said corresponding one of said passages. The array of light emitting diodes of claim 1 comprising a submount in direct contact with a conductive material. 9. The submount comprises silicon.
An array of light emitting diodes according to. 10. The submount includes a passage portion, and the first electrical contact and the second electrical contact in the one light emitting diode of the light emitting diodes are electrically conductive via the passage portion. 9. An array of light emitting diodes according to claim 8 electrically connected to the sex traces. 11. A method of forming an array of light emitting diodes, comprising: disposing a dielectric layer having a plurality of electrically conductive traces formed on a metal base layer; and forming a plurality of passes through the dielectric layer. A step of forming a portion, each of the passage portions exposing the metal base layer, a step of introducing a heat conductive material into thermal contact with the metal base layer into each of the passage portions, Disposing each of the light emitting diodes on a corresponding one of the passages, wherein each light emitting diode is in thermal contact with the heat conductive material in the corresponding passage, and Electrically connecting, for each of the light emitting diodes, a first electrical contact and a second electrical contact to separate each of the thermally conductive traces. Wherein the. 12. The method of claim 11, wherein the metal base layer has a thickness greater than about 0.01 inch. 13. The thermally conductive material in at least one of the passages, the thermally conductive material in the plurality of conductive traces and the first and the second in the corresponding light emitting diode of the light emitting diodes. The method of claim 11, comprising electrically insulating from two electrical contacts. 14. The method of claim 11, comprising introducing a solder material into at least one of the passages. 15. The method of claim 11, comprising placing at least one of the light emitting diodes in direct contact with the thermally conductive material in the corresponding passage. 16. The method of claim 11, wherein the thermally conductive material in at least one of the passages is in direct contact with the metal substrate. 17. A step of disposing a submount between one light emitting diode of the light emitting diodes and the corresponding one of the passage portions, the submount being one of the passage portions. 12. The method of claim 11, comprising direct contact with the thermally conductive material at the corresponding passage of the. 18. The method of claim 17, comprising forming the submount from silicon. 19. The step of forming a passage in the submount, wherein the first electrical contact and the second electrical contact in the one light emitting diode of the light emitting diodes form the passage. 18. The method of claim 17, comprising electrically connecting to the electrically conductive trace via.